The present invention relates to compositions useful for inducing alignment of a liquid crystal medium with polarized light and liquid crystal display elements.
Most liquid crystal devices, including displays, have a finite pre-tilt angle, controlled, for instance, by the mechanical buffing of selected polymeric alignment layers. Liquid crystal. molecules in contact with such a layer align parallel to the buffing direction, but not exactly parallel to the substrate. The liquid crystal molecules are slightly tilted from the substrate, for instance, by about 0.5-15xc2x0. For most display applications, a finite and uniform pre-tilt angle of the liquid crystal is desirable. For other display applications requiring predominately homeotropic alignment of liquid crystals, a much higher pre-tilt angle is desired, for instance, 85-89.9xc2x0. In these cases, controlling the pre-tilt by a mechanical rubbing process is very difficult.
A new process for aligning liquid crystals with polarized light was disclosed in U.S. Pat. No. 4,974,941 entitled xe2x80x9cProcess of Aligning and Realigning Liquid Crystal Mediaxe2x80x9d. Controlling the pre-tilt angle of liquid crystals in contact with optical alignment layers. while maintaining high uniformity of alignment, is an important requirement for optical alignment materials. Continuing effort has been directed to the development of compositions for optical alignment of liquid crystals and liquid crystal displays.
The present invention provides polarizable fluorinated amines of the general formula I
Pxe2x80x94Lfxe2x80x94Axe2x80x94(NH2)qxe2x80x83xe2x80x83I
wherein A is a divalent or trivalent organic moiety, Lf is a divalent organic radical comprising at least four fluorinated carbon atoms; P is a polar group comprising a Pi electron system containing at least one heteroatom selected from the group N, O and S; and q is 1 to 2.
The invention also provides a polyamic acid composition which is the reaction product of an amine component and a tetracarboxylic dianhydride component which comprises at least one structural element of each of formulas IV and V 
wherein X4 is an electron withdrawing group having a positive "sgr", A is a trivalent organic moiety, P is a polar group comprising a Pi electron system containing at least one heteroatom selected from the group N, O, and S, and Lf consists essentially of:
xe2x80x94Xxe2x80x94(CH2)nxe2x80x94(CF2)pxe2x80x94(CH2)nxe2x80x94Xxe2x80x94
wherein xe2x80x94(CF2)pxe2x80x94 is a straight chain or branched chain perfluoroalkyl radical, p is 4 to 20, X is selected from the group consisting of xe2x80x94CH2Oxe2x80x94, xe2x80x94CH2Sxe2x80x94, xe2x80x94CH2NRxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94NRxe2x80x94 and a covalent bond, wherein R is a C1-C4 hydrocarbon, n is up to 4 and M is a tetravalent organic radical derived from said tetracarboxylic dianhydride containing at least two carbon atoms, no more than two carbonyl groups of the dianhydride being attached to any one carbon atom of the tetravalent radical.
The invention further provides polyimides derived from the polyamic acids and liquid crystal display elements made with the polyimide compositions.